Polyimide compounds, due to their high thermostability and excellent insulating property, mechanical strength and resistance to chemical corrosion, are applicable in various electronic materials, such as thermostable heat-resistant circuit boards, high-temperature binders, copper clad laminates, adhesive materials of coating copper foil and the like.
However, most imide compounds are soluble only in aprotic polar solvents with high boiling point, such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide and etc, but are insoluble in organic solvents with low boiling point due to their imide structure. It is very difficult to remove aprotic polar solvents with high boiling point from the other components; therefore these solvents are usually retained in final products, resulting in increased difficulty in future processing of the products. In another aspect, since the imide compounds are less soluble in common organic solvents with low boiling point, they are difficult to be used in combination with other compounds or polymers, which highly restricts their application in industry.
It was also reported by Soo-Young Park; Seung-Woo Lee and Tae-Jin Oh (J. Appl. Polym. Sci., 2006, 102, 640) that process control of a polymer compound can be improved and simplified by introducing a cyano group (—CN) on the phenylene rings thereto to increase its solubility in polar organic solvents. Frank W. Mercer; Martin T. Mckenzie; and Maria Bruma (Burkhard. Schulz. Polym. International, 1993, 33, 4, 399) disclosed that a polymer compound may have increased glass transition temperature, dielectric constant and changed electrochemical properties when a cyano group (—CN) is introduced on the phenylene rings thereto to provide it strong electron-withdrawing property. It was also disclosed by G. P. Cao; W. J. Chen and X. B. Liu (Polymer Degradation and Stability, 2008, 93, 739) that a polymeric material may have improved thermo-oxidative resistance, flame retardancy, oxidative stability, char yield, and processability by introduction of cyano (—CN) groups on the phenylene ring thereto.
However, it is still desirable to develop a modified imide compound which has excellent solubility in common solvents, including those with low boiling points, and can impart higher toughness to the products made therefrom, so as to improve its applicability in industry.